The present invention relates to a coin discriminating device.
Heretofore, there have been coin discriminating devices, for example as shown in Japanese Laid-Open Patent Publication No.111587/1984.
This coin discriminating device includes primary and secondary coils arranged on opposite sides of a coin passage and is adapted to carry out the discrimination of the genuineness of a coin by inputting, via an amplifier, the voltage, induced in the secondary coil when the primary coil is excited by an oscillation circuit, to a comparator and then by comparing the induced voltage with a reference voltage predetermined with reference to each coin type (or coin material).
The level of the signal inputted to the comparator is influenced by drift and the thermal characteristics of the amplifiers used for the oscillation circuit to drive the primary coil and for amplifying the signals of the secondary coil and also by the aging of the amplifiers and coils. For overcoming this problem, one way is to expand the allowable range of the reference voltage in the comparator in anticipation of the level variation of the input signal. However, expansion of the allowable range of the reference voltage can often erroneously discriminate a counterfeit coin as a genuine one.